Ceramic dielectric compositions comprising calcium, lanthanum and lead titanates

ABSTRACT

A ceramic dielectric composition consisting essentially of 45 to 95 mol percent of calcium titanate, 1 to 40 mol percent of lead titanate and 1 to 20 mol percent of lanthanum titanate is advantageous for use in temperature-compensating capacitors. Addition to the basic composition of 0.1 to 5 percent by weight of Ta2O5, WO3 or CdO has the effect of broadening the temperature range for maturation, thus facilitating control of the firing conditions in the manufacture of the ceramic body.

United States Patent Yoshioka et a1.

[ 1 May 2,1972

[54] CERAMIC DIELECTRIC COMPOSITIONS COMPRISING CALCIUM, LANTHANUM ANDLEAD TITANATES [72] Inventors: Tsunehiko Yoshioka; Hisashi Satou, bothof Hirasawa, Nikaho-machi, Yuri-gun, Akita-ken; Naoki Suda,Kisagata-machi, Yuri-gun, Akita-ken, all of Japan [73] Assignee: TDKElectronic Co., Ltd., Tokyo, Japan [22] Filed: June 13,1969

[211 Appl. No.: 832,988

[30] Foreign Application Priority Data June 25, 1969 Japan ..43/43659June 25, 1969 Japan ..43/43660 [52] US. Cl. ..l06/39 R, 106/46, 252/520[51] Int. Cl. ..C04b 33/00 [58] Field of Search 106/39 R, 46; 252/63.5,507, 252/509, 520; 317/258 Primary Examiner-James E. Poer AssistantExaminer-W. R. Satterfield Attorney-Wenderoth', Lind & .Ponack 57 IABSTRACT A ceramic dielectric composition consisting essentially of 45to 95 mol percent of calcium titanate, 1 to 40 mol percent of leadtitanate and 1 to 20 mol percent of lanthanum titanate is advantageousfor use in temperature-compensating capacitors. Addition to the basiccomposition of 0.1 to 5 percent by weight of Ta O W0 or CdO has theeffect of broadening the temperature range for maturation, thusfacilitating control of the firing conditions in the manufacture of theceramic body.

9 Claims, 4 Drawing Figures 7 max-r2 I972 3.660.124

sum ESP 3 IN VENTORS TSUNEHIKO YOSHIOKA HISASHI SATOU NAOKI SUDAATTORNEYS PATENTEUf-L-W 2 m2 SHEET 3 OF 3 wi w flaw ATTORNEYS molpercent component CaTiO 90.5 MgTiO, 3.0 La,o,-2Tio, 6.5

oxidizing atmosphere at l,380 C. The ceramic body thus obtained showedthe characteristics:

Dielectric Constant 153.0 Temperature Coefficient of Capacitance -796X l'/C Q-value 3730 where the measurements were made at 25 C. and at afrequency of 1 MC/s. The temperature coefficient was measured in thetemperature region from 30 to +85 C., where the capacitance was found tochange linearly'with-temperature.

The dielectric properties of a number of ceramic compositions accordingto this aspect of the present invention produced by the proceduressimilar to those adopted in the above example are tabulated in Table l.

TABLE 1 Temperature Composition (mol percent) Dielectric coefficientconstant 0i Capacitance Number CaTiOz PbTi03 LBZOiLZTiOg (e) (X10- C.)Q-valuc 74. 0 1s. 1 0. u 153. u 490 a, :30

73. 0 16.7 10.3 155. 5 -"96 ti, 380 65. 0 24. (J 11. 0 176. 5 -J27 4,540 75. 0 17. 2 7. 8 173. 5 943 6, 810

to which is added 0.2percent by weight of MnCo The fired body of thiscomposition exhibits the following characteristics:

Dielectric Constant 130 Temperature Coefficient of Capacitance Q-valueThe fundamental object of the present invention, in one aspect thereof,is to provide ceramic dielectric compositions with more advantageousdielectric properties compared with those hitherto utilized astemperature-compensating capacitors. The ceramic dielectric compositionsof the present invention are based on the ternary system comprisingcalcium titanate, lead titanate and lanthanum titanate. A ceramic bodyhaving a dielectric constant up to 300 with the temperature coefficientranging from -700 to 2,200 X l0/ C. and a Q- value up to 7,000 isobtained by a combination of the said ingredients within the followingrange of proportion: 45 to 95 mol percent calcium titanate, l to 40 molpercent lead titanate and l to mol percent lanthanum titanate.

The ceramic body of this aspect of the present invention is produced bythe following procedure:

The raw materials are first mixed, pre-sintered in an oxidizingatmosphere, then ground to a powder. The powder is pressed into adesired shape with the addition of a suitable binder, then fired againto maturity in an oxidizing atmosphere at a temperature of l,200 to 1,380 C.

The following example is given for the better understanding of thisaspect of the invention.

EXAMPLE 1 v The raw materials, titanium oxide, calcium carbonate, leadmonoxide and lanthanum oxide were weighed so that the fired body wouldhave the composition:

mol percent component ca'rio, -74.0 who, 16.1 La,o,-2rio, 9.9

The ternary diagrams of FIGS. 1 to 4 show how the dielectricpropertiesof a ceramic body produced by the method similar to that employedinExample 1 vary as a function of the composition.

The Q-values for various compositions are given in FIG. 1, where theproportion of each of the end-members calcium titanate, lead titanateand lanthanum titanate is given in mol percent. The numerical value oneach point 'of the diagram indicates the Q-value of the correspondingcomposition. The diagram of FIG. 2 shows how the dielectric constantdepends on the composition, while FIG. 3 shows the temperaturecoefficient of capacitance measured in the temperature range from 30 toC. and the values are given in lO'/ 8c C. FIG. 4 shows how thedielectric constant of a ceramic body which has a given value of thetemperature coefficient of capacitance varies as a function of .thefraction of calcium titanate. The numerical value attached to each ofthe solid curves in the figuredenotes the temperature coefficient in l0/v C.

From the data on the dielectric properties shown in the ex ample, Tablel and the accompanying drawings, it is seen that the most favorableproperties are achieved by the combination of 75.0 mol percent calciumtitanate, 17.2 mol percent lead titanate and 7.8 mol percent lanthanumtitanate or compositions around this proportion.

Desirably, the composition of the present invention is limited to thefollowing range:

component mol percent CaTiO 45 to PbTiO l to 40 na o -z'rio m 20 To bemore exact, a composition belonging to the area of the ternary diagramenclosed by the points of the composition as A-B-C-D-E-F is mostdesirable, where the points from A to F are defined as follows:

Composition (mol The reasons for limiting the composition to the saidrange are: .When the amount of lanthanum titanate exceeds 20 molpercent, vitrification of the body becomes difficult. When the amount oflead titanate is over 40 mol percent, the Q-value would becomeunfavorably low, while the inclusion of calcium titanate in excess of 95mol percent results in the decrease of the dielectric constant to anextent no more favorable in comparison with ceramic dielectric materialshitherto utilized as temperature-compensating capacitors.

The present invention, in the precedingly-describedaspect thereof, thusprovides ceramic dielectrics with'high dielectric constant advantageousnot only in the reduction of the size of capacitors but also in thereduction of the cost needed for shaping and other processes.

While a ceramic body with favorable properties can be obtained by thebasic composition only, according to a second aspect of the invention,the addition of one of the metal oxides, tantalum oxide (Ta,0.-,).tungsten oxide (W and cadmium oxide, in small amount (0.1 to 5 percentby weight) has the effect of broadening the temperature range formaturation, thus making the control of the firing condition easier. Aceramic .body thus produced has a dielectric constant up to 300 with auniform temperature coefficient ranging from 700 to 950 X l0/ C. in thetemperature range of 30 to 85 C. 'and a Q-value up to 7,000.

The following examples are given for the better understanding of thesecond aspect of the present invention.

EXAMPLE 2 The raw materials were weighed according to the composition:

p mol percent 'CaTiO, 74.0 PbTiO, 16.1 La O 'QTiO 9.9

to which are added tantalum oxide (Ta O in amount corresponding to 0.5percent by weight of the total weight of the above components. Theingredients were thoroughly mixed,

Dielectric constant 153.0

Temperature coefficient of capacitance 796Xl0/C (30C to 85C) Qvalue 3730where the measurements'were performed at 25 C. and at a frequency of lMC/s.

Table 2 shows the characteristics of a number of ceramic compositionsaccording to the present invention produced by the method similar tothat described in the preceding example and measured also under the sameconditions as given in the As in the firstaspect of the invention, thediagrams of FIGS. 1 to 3 show how the dielectric properties of -aceramic body according to the said aspect produced by the method similarto that of Example 2 vary as a function of composition. The Q- values ofvarious ceramic compositions are shown in FIG. 1.

The end-members of the ternary diagram are calcium titanate (CaTiO leadtitanate (PbTiO and lanthanum titanate (La O -TiO of which theproportion is given in mol percent. The numerical value at each point ofthe diagram denotes the Q-valuev of the corresponding ceramiccomposition. FIG. 2 shows how the. dielectric constantdepends on thecomposition and FIG. 3 shows how thetemperature coefficient ofcapacitance measured in the temperature range from 30 to C. varies as afunction of composition, where the values are given in l0fl C.

From the data on the di electric properties shownin Example 2, Table land the accompanying drawings, it isseen that the most favorableproperties are achieved by the combination of 75.0 mol percent calciumtitanate (CaTiO 17.2 mol percent lead titanate (PbTiOa), and 7.8 molpercent lanthanum titanate (La O -2TiO or compositions in this vicinity.I

As in the first aspect, the composition of the second aspect of theinvention is limited to the following range:

mol percent CaTiO, 45 to PbTiO 1 to 40 La O,'2 TiO l to 20 but,according to the second aspect, there is added one of the metal oxidestantalum oxide T3 0 tungsten oxide (W0 or cadmium oxide (010) in anamount of 0.1 to 5 percent by weight of the total weight of thetitanates.

The reasons for limiting the composition to the said range are: When theamount ofcalciumtitanate (CaTiO is under 45 mol percent or the amount oflead titanate exceeds 40 mol percent, the Q-value becomes rather low.The inclusion of calcium titanate (CaTiO in excess of 95 mol percentresults in a low dielectric constant no more favorable compared withceramic dielectrics hitherto utilized. When the amount of lanthanumtitanate (La- O '2TiO exceeds 20 mol percent, maturation of the bodybecomes difficult. The addition of one of the said metal oxides inamount less than 0.1 percent by mol percent CaTiO, 73 .0 PbTiO 16.7La,0;,-2Ti0 10.3

are shown by the following tabulation, demonstrating that the sinteringtemperature changes effectively as follows:

additive weight percent sintering H temperature (C) none 0 1330 to 1350Ta O 3 1300 to 1330 CdO 3 1300 to 1340 WC; 3 1280 to l 320 The presentinvention thus makes it'possible to product cxamp]e 65 readily maturableceramic dielectric materials which possess TABLE 2 CompositionTemperature CaT1O PbT103, 'Ia O Dielectric coeflicient 01 mol molLflg03-2T10z, weight constant capacitance Number percent percent molpercent percent (2) (XlO- C.) Q-value 74. 0 16. 1 0. 9 0. 6 153. 0 -7l1;3, 730 73. 0 16.7 10. 3v 0.5 155.5 -7!lli 1;, 3X0 b5. 0 24. 0 11. 0 0. 5176. 5 -.127 4, 540 76. 0 17. 2 7. 8 0. 5 173. 5 +043 6, 810

. values of temperature coefficient, suitable for use as capacitors fortemperature compensation.

What is claimed is:

1. A fired ceramic dielectric composition characterized by a temperaturecoefficient ranging from .700 to -2,200 X C. over the temperature rangeof 30 to 85 C. consisting essentially of 45 to 95 mole percent calciumtitanate, l to 40 mol percent lead titanate and l to mol percentlanthanum titanate.

2. A fired composition according to claim 1, and further containingtantalum oxide, tungsten oxide or cadmium oxide in an amountcorresponding to 0.1 to 5 percent by weight of the total weight of thesaid metal titanates.

3. A fired composition according to claim 1 wherein the mo] percent ofcalcium titanate is 74.0, the mol percent of lead titanate is 16.1 andthe mol percent of lanthanum titanate is 9.9. v

1 4. A fired composition according to claim 1 wherein the mol percent ofcalcium titanate is 73.0, the mol percent of lead titanate is 16.7 andthe mo] percent of lanthanum titanate is 10.3.

5. A fired composition according to claim 1 wherein the mol percent ofcalcium titanate is 65.0, the mol percent of lead titanate 24.0 and themol percent of lanthanum titanate is 6. A fired composition according toclaim 1 wherein themol percent of calcium titanate is 75.0, the molpercent of lead titanate is 17.2 and the mol percent of lanthanumtitanate is 7.8.

7. A fired composition according to claim 6 which also contains tantalumoxide in an amount of 0.5 weight percent based on the total weight ofthe metal tita'nates.

8. A fired composition according to claim 4 which further containscadmium oxide in an amount of 3 weight percent, based upon the totalweight of the metal titanates.

9. A fired composition in accordance with claim 4 which further containstungsten oxide in an amount of 3 weight percent, based upon the totalweight of the metal titanates.

2. A fired composition according to claim 1, and further containingtantalum oxide, tungsten oxide or cadmium oxide in an amountcorresponding to 0.1 to 5 percent by weight of the total weight of thesaid metal titanates.
 3. A fired composition according to claim 1wherein the mol percent of calcium titanate is 74.0, the mol percent oflead titanate is 16.1 and the mol percent of lanthanum titanate is 9.9.4. A fired composition according to claim 1 wherein the Mol percent ofcalcium titanate is 73.0, the mol percent of lead titanate is 16.7 andthe mol percent of lanthanum titanate is 10.3.
 5. A fired compositionaccording to claim 1 wherein the mol percent of calcium titanate is65.0, the mol percent of lead titanate 24.0 and the mol percent oflanthanum titanate is 11.0.
 6. A fired composition according to claim 1wherein the mol percent of calcium titanate is 75.0, the mol percent oflead titanate is 17.2 and the mol percent of lanthanum titanate is 7.8.7. A fired composition according to claim 6 which also contains tantalumoxide in an amount of 0.5 weight percent based on the total weight ofthe metal titanates.
 8. A fired composition according to claim 4 whichfurther contains cadmium oxide in an amount of 3 weight percent, basedupon the total weight of the metal titanates.
 9. A fired composition inaccordance with claim 4 which further contains tungsten oxide in anamount of 3 weight percent, based upon the total weight of the metaltitanates.